1. Field of the Invention
The present invention relates to a portable, internal combustion-engined tool, in particular, to a setting tool for driving fastening elements in different objects, and to a method of driving the piston of such a tool.
2. Description of the Prior Act
A tool of the above-described type and a method of driving its piston is disclosed DE 40 32 202 A1. The known tool has a combustion chamber which is separated in two chamber sections arranged one after another with a separation plate having a plurality of through-openings. Upon expansion of the chamber section, air-fuel gas mixture is aspirated therein. The air-fuel gas mixtures in the chamber sections may have, respectively, different air/fuel gas rations. The combustion of the air-fuel gas mixture is started in a first, remote from the piston, chamber section with an electrical spark, and a flame front starts to spread, in this chamber section, from the center out with a relatively slow velocity. The flame front pushes the non-combusted air-fuel gas mixture away from itself, and the non-combusted air-fuel gas mixture penetrates through the openings in the separation plate into adjacent chamber section, causing there turbulence and precompression of the air-fuel gas mixture that fills this chamber section. When the flame front reaches the through-openings of the separation plate, the flame, due to the relatively narrow cross-section of the openings, penetrate into the adjacent, main chamber section in form of flame jets, creating their further turbulence. The mixed, turbulent air-fuel gas mixture in the another, main chamber section is then ignited over the entire surface of the flame jets, and burns with a very high speed. This results in a sharp increase in the effectiveness of combustion in the main chamber section, as cooling losses remain small.
After the fastening element has been driven in, and the air-fuel gas mixture in the main chamber section, which adjoining the piston, has burnt, the piston can be brought into its initial position again as a result of underpressure behind the piston which results from cooling down of the exhaust gas or the flue gas which remains in the combustion chamber and in the expansion volume of the guide cylinder. Thereafter, the exhaust gas is vented out of the combustion chamber, and a new portion of the air-fuel gas mixture is aspirated into the combustion chamber upon next expansion of the chamber sections. The air-fuel gas mixture is fed into the chamber sections having different sizes and is fed from one chamber section into another.
In conventional tools, the fuel gas in a liquid form is fed through a conduit into a pre-evaporation chamber and is mixed their with air in accordance with a desired mixture ratio. Then, the air-fuel gas mixture is fed from the pre-evaporation chamber through a conduit into the tool combustion chamber at the beginning of the setting process, i.e., upon pressing the tool against an object. The air-fuel gas mixture is fed into the combustion chamber as a result of a suction effect produced by the expansion of the combustion chamber sections. As the pre-evaporation chamber is exposed to the surrounding temperature and pressure, different air-fuel gas mixtures can be formed in the pre-evaporation chamber dependent on the parameters of the temperature and pressure. Accordingly, it is not always insured that air-fuel gas mixture fed into the combustion chamber has a desired mixture ratio. It can occur that the air-fuel gas mixture in the chamber section, which contains the ignition device, is too lean, which reduces the possibility of ignition of the mixture and thereby, the operational reliability of the tool. A too lean air-fuel gas mixture in the main chamber can lead to a reduced effectiveness.
On the other hand, with conventional tools, in particular, at low temperatures and a rapidly repeated setting process, there exists a danger that the fuel gas, which is fed into the pre-evaporation chamber in a liquid form, cannot be adequately evaporated. This results in building of ice in the gas conduit leading to the pre-evaporation chamber, and it cannot be excluded that fuel gas will remain in the pre-evaporation chamber. This again would result in a lean mixture ratio of the air-fuel gas mixture and would result in problems discussed above. Further, at the next setting process, the fluid flue gas, which accumulates in the pre-evaporation chamber, can evaporate, and as a result, taking into account the newly fed amount of the fuel gas, a too rich mixture ratio would be obtained, which can lead to fluctuation of the operational characteristics of the tools.
Accordingly, an object of the present invention is to provide a tool and a method of driving its piston which would insure a higher operational reliability of the tool and its better operational efficiency.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, a tool a combustion chamber of which is separated by a separation plate having through-openings into at least two, arranged one after another, chamber sections having each at least one separate inlet, and by providing a method according to which separately adjusted combustible gas mixtures are fed into the chamber sections through their respective inlets. As discussed, according to the inventive method, the combustible gas mixture is separately adjusted in each chamber section. This permits to obtain optimal mixture ratios of the combustible gas mixture in each chamber section. As a result, a reliable course of the setting process is insured, together with high efficiency of the tool. The combustible mixture can be formed, e.g., as a mixture of air and fuel gas, as a mixture of oxygen and fuel gas, or as any other suitable mixture.
Because of the separate adjustment of the combustible mixture in each chamber section, the mixture ratio of the air-fuel gas mixture fed into the chamber section containing the ignition device, can be adjusted so that a fatter mixture is fed into this chamber section than into the remaining chamber-sections, which insured that with each actuation of the ignition device, an ignition of the mixture in the ignition device-containing chamber section takes place. On the other hand, the air-fuel gas mixture in the main chamber section, which is adjacent to the piston can be made leaner or stoichiometric, independently of the mixture ratio in the fore-chamber section, whereby a constant, high-efficient combustion takes place in the main chamber section.
The adjustment of the air-fuel gas mixture in each chamber section is effected by commonly feeding air in all of the chamber sections and feeding a respective amount of fuel gas separately into each chamber section. With this adjustment, the number of valves, which control the feeding of media in all of the chamber sections, is reduced. In addition, because metering of only the fuel gas is required, the number of adjustment parameters is likewise reduced, which simplifies the metering process.
Advantageously, the supply of air in the chamber sections is effected by suction of the air as a result of expansion of the chamber sections. Thus, no separate air-supply devices are needed. Upon expansion of the chamber sections, the combustion chamber wall and the separation plate move away from the piston, and the air streams in the chamber section in the same direction the combustion chamber wall and the separation plate move or in opposite direction.
Preferably, the fuel gas is fed into the chamber sections in a liquid form. Thus, the fuel gas evaporates only in the chamber section. This is a significant advantage because the adjustment of the mixture ratio of the air-fuel gas mixture to a predetermined or desired value is insured even if an ice accumulation in the region of the valve takes places as a result of low environmental temperatures or of high repetition speed of the setting process. This is because the liquefied fuel gas, which was fed in a respective chamber section, has sufficient time to evaporate before the start of the ignition process.
Preferably, the amount of the fed fuel gas or the liquefied fuel gas is determined by a preliminary metering of the same. Thereby, a predetermined ratio is obtained. Temperature and pressure variations of the environment practically do not affect the metered amount of the liquefied fuel gas.
Preferably, the fuel gas is fed into respective chamber sections shortly before their complete expansion. The ignition process is initiated only after the complete expansion of the chamber sections. Thus, the time period between the time the fuel gas is delivered into the chamber sections and the time of the start of the ignition process is used for evaporation of the liquefied fuel gas.
An inventive, portable, internal combustion-engined tool, in particular a setting tool for driving in fastening elements, and having a combustion chamber divided in several chamber sections, which are arranged one after another, by at least one separation plate provided with a plurality of through-openings and in which a combustible gas mixture is combusted for driving a piston, is characterized in that each chamber section has at least one separate inlet for admitting a fuel gas. Thereby, as discussed above, a separate adjustment of the combustible gas mixture in each chamber section become possible.
Basically, each chamber section can have as many separate inlets as the number of separate gas components fed into the chamber section in order to obtain a desired mixture ratio. However, only one inlet can be provided for a chamber section for metering a single gas component when one or several other gas components are fed through one or several inlets common for all of the chamber sections.
According to the present invention, at least one separation plate is provided between the piston and the opposite combustion chamber wall. The plate and the movable chamber wall move transverse to their planes in opposite direction and, in the initial position of the piston, lie approximately on each other or on the piston.
This arrangement insures that after the return movement of the piston in its initial position, the combustion chamber can be freed of waste gases by displacing the separation plate and the movable combustion chamber wall toward the piston which displacement expels the waste gases from the space between the separation plate and the movable combustion chamber wall.
According to a further embodiment of the present invention, an aeration/deaeration valve is provided in a wall region of the combustion chamber on which the separation plate lies when it is adjacent to the piston. This valve can be used for evacuation of the waste gases from the combustion chamber on which the separation plate lies when it is adjacent to the piston. This valve can be used for evacuation of the waste gases from the combustion chamber when the combustion chamber collapses and for aeration of the combustion chamber during the movement of the movable combustion chamber wall and the separation plate away from the piston. Thus, a single valve is used for aeration and deaeration of the combustion chamber which simplifies the construction of the tool.
According to an alternative embodiment of the present invention, a deaeration valve is provided in a wall region of the combustion chamber on which the separation plate lies when it is adjacent to the piston, and an aeration valve is provided in the movable combustion chamber wall. When the movable combustion chamber wall moves away from the piston, the aeration valve opens, admitting air into the chamber sections. At this point in time, the deaeration valve is completely closed. Because both valves are located on opposite sides of the combustion chamber, there is no danger during rapidly repeating setting processes that upon the displacement of the movable combustion chamber wall away from the piston, the residual or waste gases in the deaeration valve would again penetrate into the combustion chamber through the aeration valve. The provision of the two valves also insures a more precise adjustment of the mixture ratios in the combustion chamber sections.
In order to be able to completely expand the chamber sections for admitting air therein, according to a further embodiment of the present invention, the movable combustion chamber wall, upon displacement away from the piston, engages a lug associated with the separation plate whereby the separation plate is likewise displaced by the drive mechanism. Thus, then the movable combustion chamber wall is displaced away from the piston, after a certain time period, it entrains the separation plate with it which leads to expansion of both chamber sections.
The drive mechanism for displacing the combustion chamber wall and the separation plate can include at least one rod-shaped actuation member fixedly connected with the movable combustion chamber wall and extending through the separation plate and from the combustion chamber toward the front end of the tool. A plurality of actuation members can be provided, evenly distributed over the circumference of the movable combustion chamber wall, with all of the actuation members being connected with each other by an actuation ring.
When a front-side pressing sleeve of the tool is pressed against an object and is displaced rearwardly, it actuates the actuation ring which result in displacement of the movable combustion chamber wall away from the piston which, in turn, entails aeration of the chamber section. The aeration/deaeration or only deaeration valve can be located in the region of the actuation ring and be actuated thereby, so that in the course of movement of the movable combustion chamber wall, a control of the valve takes place. This significantly simplifies the construction of the tool.
In order to be able to feed a liquefied fuel gas into the chamber sections, the inlets can be provided with different nozzles connected with a common metering valve. This permits to inject different amount of the fuel gas into the chamber sections which leads to different mixture ratios of the air-fuel gas mixtures in different chamber sections.
Alternatively, the inlets can be connected with different metering valves to achieve the same object. In this case, additional nozzles can be used for injecting the liquefied fuel gas in form of a mist, which accelerates the fuel gas evaporation.
According to a still further embodiment of the present invention, the metering valves are controlled in accordance with a position of the movable combustion chamber wall or the actuation ring. This insured, with single means, that he liquefied fuel gas has sufficient-time to evaporate before the combustion chamber reaches its end position.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.